The present invention is concerned with burners for furnaces, and more particularly with a dual-purpose burner capable of utilizing either pulverized coal or liquid fuels such as heavy oil, or both simultaneously, and if desired, utilizing the mixture of pulverized coal and steam or water and atomizing it to achieve a high combustion efficiency and the prevention of atmospheric pollution.
Many types of pulverized-coal burners utilize pulverized coal as a fuel and inject the mixture of pulverized coal and primary and secondary air into a furnace for combustion, such as the renowned U.S. B & W multiple-intertube multitip pulverized-coal burner, cross-tube pulverized-coal burner and circular burner. Another type of burner utilizes liquid fuels such as heavy oil, or utilizes gas and air mixture, and injects the atomized fuel into a furnace for combustion (known as a liquid-fuel burner and gas burner respectively). These burners have been used extensively for industrial boilers. However, thus far there has never been a burner like that of the present invention having a combination of the above-mentioned functions. On the other hand, because of a world-wide energy crisis resulting in the increase in price and in a cutback in the production of petroleum, the problems of the ever-fluctuating prices and sources of supply often must be taken into consideration in the selection of fuels, liquid as oil or solid as pulverized coal, or even a combination of both, to ensure low operating cost and uninterrupted supply of fuels. Therefore, if selection anticipates, for example, pulverized coal, then an existing liquid-fuel burner must be replaced by a pulverized-coal burner or altered to burn pulverized coal, and vice versa, depending on the fuel selected. This is not only inconvenient but costly.
It is known that in pulverized-coal burners the air supplied by a blower is partially mixed with pulverized coal and acts as a conveyor therefor. However, if the mixing of pulverized coal with air is effected by means of a turbulence, pulverized coal particles tend to be thrown by centrifugal force to the inner wall surface, particularly the outlet, of the burner pipe, and adhere thereto. Thus, after a certain period of time the passage of mixed fuel into a furnace is blocked causing more energy consumption because a blower of higher power must be used to supply more excess air in forcing the mixed fuel into the furnace. Moreover, since complete combustion of the mixed fuel can not be achieved under such circumstances, more soot and ash are produced with increasing unburned combustible loss, which in turn will bring about the problem of air pollution and a waste of energy.